Porous silicon layers were activated by the addition of Zn2SiO4:Mn2+ which resulted in green or yellow luminescent samples depending on the treatment conditions. The yellow peak occurs at 575 nm and has a considerably longer decay time than the green peak, which occurs at 525 nm. It is demonstrated that the yellow luminescence comes from small particles, typically 30 nm in size, which have been crystallized in the beta-phase, while the green luminescence comes from the usual alpha-phase, which occurs with larger particles. beta-Phase appears to be the dominant phase for small particles and any condition that results in the formation of small particles gives rise to yellow emission. (C) 2002 Elsevier Science B.V. All rights reserved.